1. Field of Invention
The invention relates to a DWDM (Dense Wavelength Division Multiplexer) and, in particular, to an integrated DWDM made by using the planar waveguide manufacturing technology for processing a wide-band beam with multiple wavelengths and correcting thermal deformation.
2. Related Art
The known devices for the DWDM include: OTFF""s (Optical Thin Film Filter), AWG""s (Arrayed Waveguide Grating), fiber gratings, etc. However,
1. The OTFF has a small dependence on the temperature. But the manufacturing process is difficult and there are few channels.
2. The AWG has the strongest dependence on the temperature. The manufacturing process is difficult and there are more channels.
3. The fiber grating has a strong dependence on the temperature. The manufacturing process is difficult and there are few channels.
Although there are many other technologies being disclosed, such as the U.S. Pat. Nos. 4,784,935, 4,387,955, and 4,736,360, the optical device structures disclosed in these patents do not use the planar waveguide manufacturing technology. Therefore, the sizes of the devices are large. Even though they all have a grating, the problem of displacement in diffractive beams due to thermal deformation on the grating is still unsolved.
An objective of the invention is to provide a planar optical waveguide DWDM that has a simpler, cost-effective manufacturing process for mass production and can solve the problem of few chancels.
Another objective of the invention provides a planar optical waveguide DWDM with little dependence on the temperature.
Using the planar waveguide manufacturing technology, a grating is mounted in a planar optical path. Using beam dispersion property due to surface relief, beams with different wavelengths are diffracted into different directions, producing the spatially wavelength division phenomenon. The wide-band input beam is then divided into many narrow-band beams, which are then directed through a planar optical path into an arrayed waveguide. The beams are coupled to an optical fiber connected to the output end of the arrayed waveguide.
Since the invention uses a dense double grating and a curved surface reflector, the input beam after wavelength division can be properly focused at small bright spots. After being guided into the arrayed waveguide, the beams are connected to respective output optical fibers. As the focused bright spots of different wavelengths are spatially apart from one another, they do not interfere. Therefore, the invention has dense, multi-channel wavelength division ability. With the planar waveguide manufacturing technology, an integrated DWDM can be obtained.
An arrayed lens is further inserted on the optical path between the diffractive grating and the arrayed waveguide so that when the grating causes diffractive beam displacements from thermal deformation, the displaced beams can be corrected back to correct paths. Thus, the invention can solve the misalignment problem due to temperature variations.